Recently, electronic apparatuses, such as mobile phones, home appliances, personal computers (PCs), personal digital assistants (PDAs), LCDs, and navigation devices, have been increasingly digitized and increased in terms of processing speeds. Such apparatuses are sensitive to external stimuli. Accordingly, when even a small abnormal voltage or high frequency noise flows into an internal circuit of the electronic apparatuses from an external source, circuit failure or signal distortion may occur.
Such an abnormal voltage or high frequency noise may be caused by power noise included in a switching voltage or power voltage internally generated in the circuit, an unnecessary electromagnetic signal, an electromagnetic noise, or the like. In order to prevent such an abnormal voltage or high frequency noise from flowing into the circuit, coil components are widely used.
In particular, in the case of high speed interfaces, such as USB 2.0, USB 3.0, and high-definition multimedia interface (HDMI), a differential signal system transmitting a differential signal (a differential-mode signal) using a pair of signal lines may be employed, unlike a normal single-end transmitting system. In such a differential signal system, a common mode filter (CMF) is used as a coil component for removing common mode noise.
A normal CMF has a laminate structure including a ferrite substrate formed by sintering magnetic powder, a coil layer formed on the ferrite substrate, and a ferrite resin composite protecting the coil layer and preventing the leakage of magnetic flux formed in the coil layer.
Here, the ferrite resin composite is formed by mixing a magnetic powder and a resin. Accordingly, since the magnetic powder is dispersed in the resin, magnetic properties of the ferrite resin composite may be significantly different from those of the ferrite substrate thereunder.
Therefore, predictions of coil properties may be difficult, and the coil properties may change significantly, depending on a connection direction of a device.
In addition, since a coil-embedded insulating layer is stacked on a ferrite substrate formed of a brittle ceramic, failures, such as delamination or cracks, may occur between the insulating layer and the ferrite substrate therebelow.